INTRODUCTION: It is not clear whether in patients with the clinical suspicion of heart failure with normal ejection fraction (HFNEF) exercise assessment of diastolic function may help to unmask abnormalities not detected by resting measurements. METHODS AND RESULTS: A combined radionuclide angiographic and haemodynamic exercise study was performed to confirm definite diastolic dysfunction in hypertensive patients with exertional dyspnoea and no other detectable cause of their symptoms. Only patients with normal baseline left ventricular (LV) systolic and diastolic function parameters as evaluated by routine cardiac catheterization and transmitral Doppler echocardiography were accepted (n = 38). All parameters were compared to a control group (n = 10). Twenty-eight patients showed an abnormal elevation in pulmonary capillary wedge pressure with exercise. As a consequence of a reduced exercise stroke volume (58 +/- 13 vs. 70 +/- 12 ml/m2; P = 0.01) peak cardiac output was reduced in HFNEF (9.3 +/- 1.7 vs. 7.6 +/- 2.0 l/min/m2; P = 0.02). These changes were equally demonstrable in patients with and without ventricular hypertrophy. LV end-systolic wall stress (ESWS) was increased at rest and during exercise in HFNEF patients without hypertrophy. However, a positive relationship between ESWS and the corresponding exercise stroke volume (r = 0.57; P = 0.002) was observed in the entire HFNEF group. CONCLUSION: Detection of diastolic dysfunction in suspected HFNEF is not only a question of the diagnostic methods used, but of the conditions under which the patients are investigated.